Vehicle cruise control systems are well known. Typically a vehicle driver is provided with the possibility to enable such a system on demand, for example via a button or stalk mounted switch. Once enabled, the vehicle will endeavour to automatically maintain a pre-set road speed regardless of road gradient. The vehicle driver is typically provided with functionality to permit the pre-set road speed to be adjusted up or down, to cancel cruise and to resume cruise; cruise may also be cancelled in the event of a driver input, in particular braking.
In a vehicle with an automatic multi-speed transmission, the cruise function may also select an appropriate speed ratio, for example a downshift upon sensing a significant up gradient.
If the vehicle encounters a down gradient with cruise selected, the frictional forces acting to reduce vehicle speed may be insufficient to counter the natural tendency for the vehicle to gain momentum and thereby increase speed.
If the down gradient is significant the vehicle may gradually increase speed even if fueling of the engine is ceased. In such circumstances it has been proposed to provide automatic braking whereby the vehicle brakes are actuated to reduce speed so that the pre-set vehicle speed is maintained.
Automatic vehicle braking is typically a complex and relatively expensive vehicle system; what is required is a relatively simple means of reducing vehicle speed, which is intuitive, and which is intelligent.